The contracts are estimated to equate to over a third-of-a-million bottles a year being bought from the company near Llandeilo.
Brecon Carreg marketing manager, Gill Bullock, said, "Bmi is one of the UK's largest full-service scheduled airlines and bmibaby is one of the market leaders in the low-cost arena. Both airlines cater for a diverse range of passengers, including families.
"Brecon Carreg is an affordable and popular product with the family market, making the relationship a good fit for both parties... Most importantly, it will help keep people hydrated while they fly."
The importance of drinking water in flight is increasingly stressed in information campaigns. The amount of fluid evaporation from the body rises at higher altitudes and in dry environments, which means people are more likely to become dehydrated when flying.
The two companies first met at a Cardiff Blues function, proving that their loyal support of the team pays off.